Various methods are already known for increasing the security of roll-down shutters. One such method consists of a self-locking winding shaft that is provided with a worm drive which is only rotatable by a hand crank or a motor, that can be self-turned by a motor cutoff or hand-crank and not by attacking the winding shaft. A suitable formation of the top-most shutter element together with subsequent shutter elements (usually in a shutter box), prevents any unauthorized pushing up of the shutter armor. A previous weakness was the attachment of the top-most shutter element onto the exhaust-shaft, that previously resulted from screwing or bolting. After opening the shutter box, it was thus possible for an intruder with relatively simple tools to loosen the top-most shutter element from the winding shaft thereby pulling the shutter armor away despite the shaft being in the locked position.